1. Field of the Invention
The present invention relates to a process and apparatus for recovering hydrocarbons from inert gas-hydrocarbon vapor mixtures, and more particularly, but not by way of limitation, to an improved process and apparatus for recovering vaporized gasoline light ends and the like from a mixture thereof with air or other inert gas.
2. Description of the Prior Art
In handling multicomponent hydrocarbon liquids such as gasoline, kerosene, solvents and the like, mixtures of hydrocarbon vapors and inert gases such as air, nitrogen, etc., are often produced which cannot be vented directly to the atmosphere due to the resulting pollution of the environment and the fire and/or explosion hazard. Consequently, a variety of processes and apparatus have been developed and used heretofore for removing hydrocarbon vapors from inert gas-hydrocarbon vapor mixtures whereby the remaining inert gas can be vented to the atmosphere or reused. The removed hydrocarbons are generally liquefied and recombined with the hydrocarbon liquids from which they were vaporized thereby making the recovery economically advantageous.
The term "inert gas" is used herein to mean a gas which does not react with hydrocarbons to a substantial degree and which is not readily adsorbed on beds of solid adsorbent having an affinity for hydrocarbons or readily absorbed in liquid absorbents having an affinity for hydrocarbons. Examples of such inert gases are oxygen, nitrogen, air and the like. For purposes of this disclosure, light hydrocarbon vapors such as methane are considered to be within the definition of "inert gas" when mixed with heavy hydrocarbon vapors such as those utilized in solvents in that while such light hydrocarbons are readily adsorbed on beds of solid adsorbent having an affinity for hydrocarbons they are also readily displaced by the heavier hydrocarbons. In addition, liquid absorbents having an affinity for heavier hydrocarbons can be utilized which do not absorb major portions of lighter hydrocarbons such as methane.
A process for the recovery of light mixed hydrocarbon vapors from an air-hydrocarbon mixture expelled as a result of storage breathing or loading of vented hydrocarbon vessels is described in U.S. Pat. No. 4,066,423 issued Jan. 3, 1978. In accordance with such process, the air-hydrocarbon vapor mixture from which hydrocarbons are to be removed and recovered is passed through a bed of solid adsorbent having an affinity for hydrocarbons. As the mixture passes through the bed, a major portion of the hydrocarbons contained in the mixture are adsorbed on the bed and a residue gas stream is produced which is comprised substantially of hydrocarbon-free air. The hydrocarbon-rich air-hydrocarbon mixture produced as a result of the evacuation regeneration of the bed is contacted with a liquid absorbent whereby hydrocarbons are removed therefrom and the residue gas stream from the absorption step is recycled to the bed through which the inlet air-hydrocarbon mixture is flowing. In accordance with the teachings of U.S. Pat. No. 4,066,423, the liquid absorbent utilized is comprised of liquid hydrocarbons condensed from the air-hydrocarbon vapor mixture produced in the evacuation regeneration step. The use of hydrocarbons which are condensed from the hydrocarbon-rich air-hydrocarbon vapor mixture to contact the remaining air-hydrocarbon vapor mixture results in the inefficient absorption of hydrocarbons from the remaining air-hydrocarbon vapor mixture. In addition U.S. Pat. No. 4,066,423 teaches the use of a liquid ring vacuum pump for evacuating the bed of solid adsorbent being regenerated. The use of such a pump requires elaborate three-phase separation apparatus for separating gases and condensed hydrocarbons from the sealing liquid used as well as apparatus for cooling the sealing liquid which is recirculated to the vacuum pump.
U.S. Pat. No. 4,261,716 issued Apr. 14, 1981, and U.S. Pat. No. 4,276,058 issued June 30, 1981, are directed to processes and apparatus for recovering hydrocarbons from air-hydrocarbon vapor mixtures, and while such processes and apparatus overcomes the problem with inefficient absorption of hydrocarbons from the hydrocarbon-rich air-hydrocarbon vapor mixture mentioned above in connection with U.S. Pat. No. 4,066,423, and are more efficient in removing and recovering hydrocarbons from inlet air-hydrocarbon vapor mixtures, they also disclose that a liquid seal vacuum pump is preferred for use in the apparatus.
Numerous other processes and apparatus for recovering hydrocarbons from air-hydrocarbon vapor mixtures or otherwise treating said mixtures as disclosed in U.S. Pat. Nos. 3,897,193; 3,979,175; 3,867,111; 3,768,232; 3,455,089; 3,543,484; and 3,776,283.
By the present invention, an improved process and apparatus for recovering hydrocarbons from inert gas-hydrocarbon vapor mixtures is provided which overcomes the problem mentioned above, which is more efficient and which is less expensive than the heretofore used process and apparatus.